CR Domains Research Articles

Microstructures of Co/Cr Bilayer Films Epitaxially Grown on MgO Single-Crystal Substrates

Microstructures of Co/Cr bilayer films epitaxially grown on MgO (100) and (110) single-crystal substrates have been studied by high-resolution transmission electron microscopy. The bicrystalline Co layer formed on the MgO (100) substrate contains a number of (0001) stacking faults. The single-crystal Co layer formed on the MgO (110) substrate consists of slightly misoriented subgrains, grown on (211)-oriented Cr domains. Dislocations and lattice strain are observed at the Cr/MgO (110) interface. The misorientations and the defects are thought to be introduced to accommodate the large lattice mismatch of about -16% in the MgO [1̄10] direction at the Cr/MgO (110) interface.

Epitaxy of thin Cr layers on Cu(001)

Thin Cr films (6–30 monolayers) have been evaporated in ultra-high vacuum onto a Cu(001) single crystal kept at room temperature and have been studied by low energy electron diffraction (LEED), X-ray photoelectron diffraction (XPD), and angle resolved ultra-violet photoemission (ARUPS). The LEED diagrams obtained for these layers reveal the formation of epitaxial body-centered cubic (bcc) Cr domains with Cr(110)‖Cu(001) and Cr[11̄1̄]∥Cu[110]. The Cu(001) substrate symmetry results in four different orientations of these domains. This conclusion is confirmed by the XPD data. Indeed the modulations of the Cr 2p 3 2 core level intensity as a function of emission angle are in agreement with single scattering simulations performed for a superposition of equivalent bcc Cr(110) domains on a Cu(001) substrate. Moreover, ARUPS results at normal emission also indicate that the Cr film exposes a (110) surface.

Epitaxial growth of fcc Cr on Au(100).

Synchrotron x-ray diffraction and anomalous dispersion measurements of 25A Cr layers epitaxially grown on (100) Au surfaces indicate the presence of fcc Cr domains, while extended x-ray absorption fine-structure spectra are consistent with the usual bcc phase of Cr. Together these data suggest that the fcc phase is a major fraction of the larger epitaxial Cr domains, but that most Cr atoms are in a bcc environment with much smaller domain sizes. This unusual, epitaxially stabilized fcc Cr structure may be related to previously reported low-temperature resistance anomalies.

Supported chromium oxide catalyst for olefin polymerization: IV. Physico-chemical study of the activation process

Both magnetic susceptibility and oxygen chemisorption measurements on chromium oxide supported on silica-alumina catalyst show a limited evolution of the dispersion state of the chromium oxide during the time of the activation treatment in air at 550 °C. The Cr(III) domains tend to be more isotropic, and the reverse is true for the Cr(VI) domains. However, the activity for ethylene polymerization is only slightly stabilized by a longer activation time.